US5911907A - Composition and method for stripping tin and tin-lead from copper surfaces - Google Patents
Composition and method for stripping tin and tin-lead from copper surfaces Download PDFInfo
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- US5911907A US5911907A US08/521,305 US52130595A US5911907A US 5911907 A US5911907 A US 5911907A US 52130595 A US52130595 A US 52130595A US 5911907 A US5911907 A US 5911907A
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F1/00—Etching metallic material by chemical means
- C23F1/44—Compositions for etching metallic material from a metallic material substrate of different composition
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K13/00—Etching, surface-brightening or pickling compositions
- C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
- C09K13/06—Etching, surface-brightening or pickling compositions containing an inorganic acid with organic material
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F1/00—Etching metallic material by chemical means
- C23F1/10—Etching compositions
- C23F1/14—Aqueous compositions
- C23F1/16—Acidic compositions
- C23F1/30—Acidic compositions for etching other metallic material
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
- H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
- H05K3/067—Etchants
Definitions
- the present invention relates to stripping tin and tin-lead alloys from copper surfaces, and more particularly, to an aqueous nitric acid-based composition and method for stripping tin and tin-lead alloys from copper surfaces such as printed circuit boards, which composition and method function in the stripping operation to inhibit exothermic conditions, emission of toxic NOx gas, copper attack, and sludge formation, while yielding a uniform, reflective, bright pink surface on the underlying copper.
- PCBs printed circuit boards
- a film or layer of tin and/or tin-lead alloy is typically plated on the conductive copper surface of the board to serve as an etch resist in the subsequent etching away of other copper surfaces. Later in the fabrication process, the tin and tin-lead must be chemically stripped from the copper circuit.
- One method of stripping tin and tin-lead from copper surfaces uses a single solution containing nitric acid and ferric nitrate. It is known that as tin or tin/lead contacts copper, tin molecules migrate into the copper, forming a copper-tin inner-metallic layer.
- a stripping solution containing nitric acid and ferric nitrate will remove both the tin or tin/lead, and the copper-tin inner-metallic layer.
- the nitric acid strips the pure tin or tin-lead off the panel, and ferric nitrate is used to aid in stripping the remaining copper-tin inner-metallic layer to bare copper.
- different materials have been added to the nitric acid/ferric nitrate stripping solution to stabilize the solution.
- the added material often increase the cost of the stripping process. In some cases, the added materials are so expensive the resultant stripping solutions are impractical to use.
- the copper circuit is exposed on the dielectric material.
- the circuit board can then be inspected using automated optical inspection, or AOI.
- AOI uses reflected light from the dielectric material and copper circuit to inspect the boards. Because the dielectric material is dull and non reflective, if the copper surface is uniform, reflective, and bright pink, AOI can easily distinguish between the dull, non-reflective dielectric material and the uniform, reflective, bright pink copper. Therefore, a uniform, reflective, bright pink copper surface increases the effectiveness of the AOI. Having a copper surface which is a non-uniform matte pink finish decreases the effectiveness of AOI.
- Sludge formation is another problem associated with conventional tin and tin/lead nitric acid-based stripping.
- tin and tin/lead stripping solutions contain dissolved metals.
- the metal loading of the stripping solution increases, the metal precipitates out of solution as sludge. It is believed that the sludge precipitate is stannic oxide.
- the sludge can cause clogging in the spray nozzles.
- the stripping solution is sprayed onto the circuit boards to strip the tin or tin/lead, sludge is also sprayed onto the boards. This sludge may be difficult to rinse off of the circuit board, leaving a white, chalky material on the board. Sludge also makes it difficult to keep conveyerized process equipment clean.
- the stripping solution when a certain metal loading level is reached, the stripping solution often becomes unstable, creating a potential for an exothermic condition, which is an instant release of a massive amount of heat.
- an exothermic condition which is an instant release of a massive amount of heat.
- large amounts of toxic NOx gas are released during an exothermic condition, and the striping solution foams excessibely.
- the temperature of the stripping solution can increase to 150° F. or greater. Obviously, the occurrence of exothermic conditions can damage the operating equipment.
- Another problem caused by conventional nitric acid-based tin and tin/lead stripping solutions is an excessive copper attack rate. Obviously it is desirable to minimize copper attack rate during tin or tin/lead stripping. A high copper attack results in stripping the copper off the circuit and exhausting the strength of the tin and tin/lead stripping solution on unnecessary copper removal. Also, process consistency is not achieved when a stripping solution has an initial high copper attack rate which drastically decreases with metal loading.
- NOx gas evolves from the nitric acid while in the presence of the tin and copper ions.
- the NOx evolving from the reaction between nitric acid and tin or tin/lead is any mixture of nitrogen dioxide and nitrogen monoxide. Both nitrogen dioxide and nitrogen monoxide are considered poisonous gases by the Occupational Safety and Health Administration. OSHA has set exposure limits on these toxic gases; the present permissible exposure level of nitrogen dioxide is 3 ppm, and the time weighted average of exposure for nitrogen monoxide is 25 ppm.
- U.S. Pat. No. 4,713,144 to Schiller discloses the use of sulfamic acid to stabilize the nitric acid stripping solution and to inhibit copper attack.
- the Schiller solution causes excessive sludge formation, and has a high potential for creating an exothermic condition.
- the Schiller method and composition leaves a non-uniform, matte pink finish on the underlying copper surface, rather than the desired uniform, reflective, bright pink appearance.
- U.S. Pat. No. 4,374,744 to Kawanabe principally addresses the problem of copper attack.
- the Kawanabe patent discloses stripping solutions consisting of an inorganic and/or organic acid, an oxidizing agent, and a heterocyclic compound free of sulfur but containing a nitrogen atom in the form of ⁇ NH or .tbd.N as a ring forming member. Examples given include imidazole and derivatives thereof and triazoles and derivatives thereof.
- the Kawanabe patent lists general categories of compounds expected to be suitable in inhibiting copper attack, such as pyrroles, pyrazoles, imidazoles, and triazoles.
- the present invention is summarized in one embodiment in a composition for stripping tin or tin-lead alloys, and any underlying copper-tin intermetallic, from a copper surface.
- the composition includes an aqueous solution of approximately 5-60% nitric acid by weight, approximately 0.5-30% ferric nitrate by weight, and a nitric acid stabilizer selected from the group consisting of an amino-triazole, an amino-isoxazole, and a linear amino sulfone in the form H 2 N--SO 2 --R, where R is any alkyl or benzene group, wherein the stabilizer is present at a concentration sufficient to inhibit exothermic conditions, emission of toxic NOx gas, and copper attack.
- a soluble source of halogen ion such as hydrochloric acid
- a soluble source of halogen ion such as hydrochloric acid
- SO 4 -2 a soluble source of sulfate ion
- the present specification describes an aqueous, nitric acid-based composition and method for stripping tin and tin-lead alloys from copper surfaces such as printed circuit boards, which composition and method function in the stripping operation to inhibit exothermic conditions, emission of toxic NOx gas, copper attack, and sludge formation, while yielding a uniform, reflective, bright pink surface on the stripped copper.
- the aqueous composition includes nitric acid present in an amount sufficient to strip the tin and/or tin-lead alloy layer of etch resist; the concentration of nitric acid typically falls in the range of about 5-60% by weight (preferably approximately 20-40% by weight).
- the composition also includes ferric nitrate in an amount sufficient to strip the remaining copper-tin inner-metallic layer which is present, which is in the range of about 0.5-30% by weight (preferably approximately 5-15% by weight).
- the composition also includes a nitric acid stabilizer present in a concentration sufficient to inhibit the critical problems exhibited by prior art stripping compositions and methods.
- the stabilizer concentration should be at least about 5 g/l, preferably in the range of about 5-30 g/l, and most preferably, about 20 g/l.
- Suitable nitric acid stabilizers include an amino-triazole (preferably 4-amino-1,2,4-triazole), an amino-isoxazole (preferably 3-amino-5-methylisoxazole), and a linear amino sulfone in the form H 2 N--SO 2 --R, where R is any alkyl or benzene group; the preferable linear amino sulfones include sulfanilamide, sulfamide, and ammonium sulfamate.
- the inventor first addressed the prior art problems of NOx emission and excessive copper attack by initially screening a number of potential stabilizing compounds to determine which showed the potential for inhibiting copper attack and eliminating emission of toxic NOx gas.
- Most of the compounds tested in the screening study and in the Examples were purchased from Aldrich Chemical Company, Milwaukee, Wis.; sulfamide was purchased from Sigma Chemical Company, St. Louis, Mo.
- Copper attack was considered acceptable if the copper etch rate on copper coupons immersed in the composition was less than 20 micro inches of copper per minute.
- NOx gas emission was considered acceptable if no orange NOx gas was visible during stripping, and unacceptable if the orange gas was visible during stripping. The following procedure was followed for screening all potential stabilizer compounds.
- An aqueous stripping composition having the following composition was made: 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, 20 grams per liter of the potential stabilizer. Copper coupons plated with tin to a thickness of 400 micro inches and copper coupons with tin/lead plated to a thickness of 350 micro inches were immersed in the stripping composition at 75° F. The copper etch rate on the coupon was measured, and the presence or absence of NOx gas was determined visually. The initial screening results are presented in Table I.
- the Kawanabe stripping solutions included an inorganic and/or organic acid, an oxidizing agent, and a heterocyclic compound free of sulfur but containing a nitrogen atom in the form of ⁇ NH or .tbd.N as a ring forming member. Examples given include imidazole and derivatives thereof and triazoles and derivatives thereof.
- an amino functional group (NH 2 ) is not bonded to the heterocyclic compound, an unacceptable amount of toxic NOx gas will be emitted during the stripping operation.
- triazole compounds lacking an amino functional group such as benzotriazole and 1,2,3-triazole, emit toxic NOx from the stripping solution while in contact with tin, tin-lead, and copper.
- benzotriazole and 1,2,3-triazole emit toxic NOx from the stripping solution while in contact with tin, tin-lead, and copper.
- the presence of an amino functional group on the triazole also results in a drastic reduction in attack on the underlying copper.
- the amino-triazole stabilizer discovered by the present inventor provides unexpectedly superior results over the general class of heterocyclic compounds free of sulfur but containing a nitrogen atom in the form of ⁇ NH or .tbd.N as a ring forming member, as described in the Kawanabe patent.
- the following Examples illustrate further study of the five stabilizing compounds identified in the initial sceening study described above.
- the Examples note tin and tin/lead strip time, copper attack, evolution of NOx for each stripping solution, and exotherm potential.
- the tin and tin/lead strip time was determined by immersing a tin or tin/lead coupon in the solution, and noting the time required to completely strip the tin or tin/lead, and the copper-tin inner-metallic.
- the copper attack was measured by immersing a copper coupon in the solution and determining the amount of copper etched by the solution.
- the evolution of NOx was determined by noting the emission of orange NOx gas.
- the solution was considered to have exotherm potential, if while loading the samples with metal, a temperature in excess of 150° F. was observed.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter sulfanilamide was made. Copper coupons plated with tin to a thickness of 400 micro inches and copper coupons with tin/lead plated to a thickness of 350 micro inches were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 8 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 60 seconds.
- the tin-lead was completely stripped off of the coupons in 45 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 4 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas. An exotherm did not occur while loading the solution.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter of 3-amino-5-methlyisoxazole was made.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 10 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 52 seconds.
- the tin-lead was completely stripped off of the coupons in 47 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 3 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas. An exotherm did not occur while loading the solution.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter of 4-amino-1,2,4-triazole was made.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 9 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 100 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas. An exotherm did not occur while loading the solution.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter of sulfamide was made.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 9 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 90 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas. An exotherm did not occur while loading the solution.
- An aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 50 grams per liter of ammonium sulfamate.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 18 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 8 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 90 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas. An exotherm did not occur while loading the solution.
- the tin-lead was completely stripped off of the coupons in 18 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched 8 micro inches of copper per minute. The copper appearance of the coupons was non-uniform, matte pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 90 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute.
- the appearance of the copper coupons was non-uniform, matte pink. There was no detectable evolution of NOx gas. An exotherm occurred while loading the solution. The final temperature after the exotherm was 155° F.
- the appearance of the copper coupons was semi-bright pink. This demonstrates that a not all heterocyclic compounds free of sulfur but containing a nitrogen atom in the form of ⁇ NH or .tbd.N as a ring forming member inhibit copper attack. Toxic NOx gas evolved during the stripping process.
- Example 6 and 7 are provided to illustrate the improvements over prior art.
- Example 6 replicates conditions disclosed in U.S. Pat. No. 4,713,144 to Schiller, and an exothermic condition occurred.
- the stabilizers of the present invention inhibit creation of an exothermic condition.
- Example 7 replicates conditions disclosed in U.S. Pat. No. 4,374,744 to Kawanabe et al. Comparing Example 3 to Example 7, it is evident that great improvements in inhibiting copper attack and toxic NOx gas evolution were achieved by using a compound which has an amino functional group bonded to the heterocyclic compound (i.e., the 4-amino-1,2,4-triazole stabilizer used in Example 3, compared to the benzotriazole stabilizer used in Example 7).
- the amino-triazole provides unexpectedly superior results over benzotriazole.
- the initial copper attack for the Kawanabe stripping solution replicated in Example 7, is 150 micro inches per minute. Such excessive copper attack results in an undesirable amount of copper removal during the tin or tin/lead stripping process.
- the Kawanabe stripping solution has a copper attack that decreases tenfold over the life of the stripping process.
- Process consistency cannot be achieved with a stripping solution that initially has a high copper attack, which significantly decreases with metal loading.
- toxic NOx gas was evolved during the stripping process from the Kawanabe stripping solution used in Example 7; NOx was not emitted during the course of Example 3, which used a composition of the present invention including the stabilizer 4-amino-1,2,4-triazole.
- the composition may also include as a brightening agent a water soluble source of halogen ion such as hydrochloric acid or the equivalent, at a concentration in the range of about 0.1%-20% by weight (preferably, 0.1%-2% by weight), to provide a uniform, reflective, bright pink appearance on the stripped copper surface.
- a brightening agent a water soluble source of halogen ion such as hydrochloric acid or the equivalent, at a concentration in the range of about 0.1%-20% by weight (preferably, 0.1%-2% by weight), to provide a uniform, reflective, bright pink appearance on the stripped copper surface.
- the following Examples further illustrate the invention.
- the Examples note tin and tin/lead strip time, copper attack, and copper appearance.
- the tin and tin/lead strip time was determined by immersing a tin or tin/lead coupon in the stripping solution and noting the time required to completely strip the tin or tin/lead, and the copper-tin inner-metallic.
- the copper attack was measured by immersing a copper coupon in the solution and determining the amount of copper etched by the solution.
- the copper appearance of the tin or tin/lead stripped coupons was determined by visual inspection of the stripped coupon.
- the copper appearance of the tin or tin/lead stripped coupons fall into several categories, non-uniform matte pink, semi-bright pink, and uniform reflective bright pink.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter sulfanilamide was made.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 8 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 60 seconds.
- the tin-lead was completely stripped off of the coupons in 45 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 4 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was improved by adding 0.2 percent by weight hydrochloric acid, as a source of halogen ion, to improve the copper appearance. There was no effect on the strippability of the stripping solution, but the appearance of the copper coupons was uniform, reflective, bright pink. There was no detectable evolution of NOx gas.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter of 3-amino-5-methlyisoxazole was made.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 10 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 52 seconds.
- the tin-lead was completely stripped off of the coupons in 47 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 3 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was improved by adding 0.2 percent by weight hydrochloric acid, as a source of halogen ion, to improve the copper appearance. There was no effect on the strippability of the stripping solution, but the copper appearance was uniform, reflective, bright pink. There was no detectable evolution of NOx gas.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter of 4-amino-1,2,4-triazole was made.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 9 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 100 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was improved by adding 0.2 percent by weight hydrochloric acid, as a source of halogen ion, to improve the copper appearance. There was no effect on the strippability of the stripping solution, but the copper appearance was uniform, reflective, bright pink. There was no detectable evolution of NOx gas.
- aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 20 grams per liter of sulfamide was made.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 15 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 9 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 90 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was improved by adding 0.2 percent by weight hydrochloric acid, as a source of halogen ion, to improve the copper appearance. There was no effect on the strippability of the stripping solution, but the copper appearance was uniform, reflective, bright pink. There was no detectable evolution of NOx gas.
- An aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 50 grams per liter of ammonium sulfamate.
- Tin plated copper coupons and tin-lead plated copper coupons, as described in example 1 were immersed in the stripping solution at 75° F. The tin was completely stripped off of the coupons in 18 seconds. The tin-lead was completely stripped off of the coupons in 18 seconds. A copper coupon was then immersed in this formula for an additional 5 minutes. It was determined that the stripping solution had etched less than 8 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 90 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute. The appearance of the copper coupons was semi-bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was improved by adding 0.2 percent by weight hydrochloric acid, as a source of halogen ion, to improve the copper appearance. There was no effect on the strippability of the stripping solution, but the copper appearance was uniform, reflective, bright pink. There was no detectable evolution of NOx gas.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 90 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched less than 2 micro inches of copper per minute. The appearance of the copper coupons was non-uniform, matte pink. There was no detectable evolution of NOx gas.
- the stripping solution of Example 13a was improved by adding 0.2 percent by weight hydrochloric acid, as a source of halogen ion, to improve the copper appearance. There was no effect on the strippability of the stripping solution, but the copper appearance was uniform, reflective, bright pink. There was no detectable evolution of NOx gas.
- the appearance of the copper coupons was semi-bright pink. This demonstrates that a not all heterocyclic compounds free of sulfur but containing a nitrogen atom in the form of ⁇ NH or .tbd.N as a ring forming member inhibit copper attack. Toxic NOx gas evolved during the stripping process.
- the above stripping solution was then loaded to 12 ounces per gallon tin, and 2.5 ounces per gallon copper.
- the tin was completely stripped off of the coupons in 90 seconds.
- the tin-lead was completely stripped off of the coupons in 75 seconds.
- a copper coupon was then immersed for an additional 5 minutes. It was determined that the stripping solution had etched 20 micro inches of copper per minute The appearance of the copper coupons was semi-bright pink. Toxic NOx gas evolved during the stripping process.
- Example 14a The stripping solution of Example 14a was improved by adding 0.2 percent by weight hydrochloric acid, as a source of halogen ion, to improve the copper appearance. There was no effect on the strippability of the solution.
- the copper etch rate was determined to be 150 micro inches of copper per minute. The copper appearance was uniform, reflective, bright pink. Toxic NOx gas evolved during the stripping process.
- Example (13a) and (14a) are provided to illustrate the improvements over prior art.
- Example (13a) replicated conditions disclosed in U.S. Pat. No. 4,713,144 to Schiller.
- An improvement in copper appearance was achieved by adding halogen ion to the Schiller composition.
- the improved uniform, reflective, bright pink copper surface increases the effectiveness of automated optical inspection over what can be achieved with the non-uniform, reflective, matte pink copper appearance which typically results from stripping with an unmodified Schiller composition.
- Example (14a) replicated conditions disclosed in U.S. Pat. No. 4,374,744 to Kawanabe et al. As was the case with modifications to the Schiller composition, improvements in copper appearance are also achieved by the addition of the halogen ion to the original Kawanabe composition.
- Sludge formation creates several problems. In spray applications, the sludge can cause clogging in the spray nozzles. When stripping solution is sprayed onto the circuit boards to strip the tin or tin/lead, sludge is also sprayed onto the boards. This sludge may be difficult to rinse off of the circuit board, leaving a white, chalky material on the board. Sludge also creates problems when cleaning equipment.
- the sludge which forms during tin and tin/lead stripping is stannic oxide.
- Stannic oxide is formed from the oxidized tin being stripped from the panels and the oxygen present in the air.
- Stannic oxide is insoluble in water and acid.
- a halogen ion such as a chloride ion
- the oxidized tin being stripped from the panels forms stannic chloride, instead of stannic oxide.
- stannic chloride is soluble in water and nitric acid. The formation of stannic chloride prevents the formation of stannic oxide sludge.
- concentration of halogen ion should be increased.
- the source of sludge-eliminating halogen ion can be any water soluble compound containing a chloride ion, such as hydrochloric acid or the equivalent, at a concentration in the range of about 0.1%-20% by weight (preferably, 1.5%-5 by weight).
- concentration of halogen ion necessary to achieve a uniform, reflective, bright pink copper surface is less than the amount of halogen ion required to eliminate the formation of sludge.
- the increased amount of halogen ion needed to eliminate sludge formation may have a negative effect on copper appearance when the bath has low metal loading (defined as a level of less than about 7 ounces tin/gal).
- metal loading defined as a level of less than about 7 ounces tin/gal.
- metal loading level greater than about 10 ounces tin/gal.
- Sludge formation can also be eliminated by adding to the composition a water soluble source of sulfate ions, such as sulfuric acid or ferric sulfate, preferably at a concentration in the range of about 0.1%-20% by weight.
- Sulfate ion does not have a negative effect on the copper appearance.
- adding a sulfate ion to the stripping solution may inhibit tin/lead alloy stripping. Therefore, it is preferred to use sulfate ion to eliminate sludge formation when a pure tin stripping process is to be performed, as opposed to stripping of tin/lead alloys.
- stannous sulfate is soluble in water and acid. The formation of stannous sulfate prevents the formation of stannic oxide sludge.
- the sulfate ion can be present in the stripping solution as part of any compound, but it is preferred to add the sulfate ion to the stripping solution as sulfuric acid and/or ferric sulfate.
- halogen ions When using halogen ions to eliminate sludge, it should be understood that at low metal loading levels, adding halogen ions to prevent sludge formation may adversely affect the appearance of the copper surface. For instance, a tin and tin/lead stripping bath which strips approximately 20 ounces per gallon of metal, would require such a large amount of halogen ion to eliminate sludge formation, a dark copper appearance would result.
- Replenishment can be performed by physically adding replenisher solution and decanting the excess solution that results, or by using an automatic controller which automatically replenishes solution.
- Automatic replenishment controllers are presently available.
- One such automatic controller is the TEKtrollerTM SG-795, commercially available through SURFACE TEK SPECIALTY PRODUCTS.
- This Example demonstrates a method for creating a sludge free stripping solution, using the stripping composition disclosed in U.S. Pat. No. 4,713,144 to Schiller.
- An aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 45 grams per liter of sulfamic acid was made. While loading this stripping sample with tin and copper, the solution had sludge formation. At 20 ounces per gallon tin and 3 ounces per gallon copper, greater than 40 percent of the solution volume was sludge.
- Another way to prevent the formation of copper oxide is to add sulfate ions to the stripping solution.
- sulfate ions when sulfate ions are present, it is difficult to strip lead from the holes of the circuit board. Therefore, it is preferred that the use of sulfate ions to prevent sludge formation, be reserved to situations when stripping pure tin.
- This Example demonstrates a method for creating a sludge free stripper, using the stripping composition disclosed in U.S. Pat. No. 4,713,144 to Schiller.
- An aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 45 grams per liter of sulfamic acid was made. While loading this stripping sample with tin and copper, sludge formed. At 20 ounces per gallon tin and 3 ounces per gallon copper, greater than 40 percent of the solution volume was sludge.
- One percent (by weight) sulfuric acid was then added to the stripping composition described above.
- the resulting modified stripping composition was loaded to 20 ounces per gallon tin and 3 ounces per gallon copper. While loading the stripping solution with tin and copper, no sludge formed. At 20 ounces per gallon tin and 3 ounces per gallon copper, there was still no sludge present. Therefore, the addition of a sufficient amount of sulfate ion prevents the formation of sludge.
- This example also demonstrates a method for creating a sludge free stripping composition, using a stripping composition as disclosed in U.S. Pat. No. 4,713,144 to Schiller.
- An aqueous stripping solution consisting of 28 percent by weight nitric acid, 7 percent by weight ferric nitrate, and 45 grams per liter of sulfamic acid was made. While loading this stripping sample with tin and copper, sludge formed. At 20 ounces per gallon tin and 3 ounces per gallon copper, greater than 40 percent of the solution volume was sludge.
Abstract
Description
TABLE I ______________________________________ Copper Evolution of Possible Stabilizer Attack NOx ______________________________________ sulfaniliamide acceptable acceptable sulfamide acceptable acceptable methanesulfonamide unacceptable unacceptable 2-aminobenzenesulfonamide unacceptable unacceptable 4-amino-6-chlor-1,3- unacceptable unacceptable benzenedisulfonamide 4- unacceptable unacceptable (aminomethyl)benzenesulfon amide N-(2-thiazolyl) unacceptable unacceptable sulfanilamide sulfisomidine unacceptable unacceptable amino-methane sulfonic unacceptable unacceptable acid 4-carboxybenzene unacceptable unacceptable sulfonamide 4-amino-1,2,4-triazole acceptable acceptable 3,5-diamino-1,2,4-triazole unacceptable unacceptable sulfisoxazole; unacceptable unacceptable sulfadiazine unacceptable unacceptable sulfamethazine; unacceptable unacceptable 3-amino-5-methylisoxazole acceptable acceptable 5-amino-3-methylisoxazole unacceptable unacceptable 4-amino-antipyrine unacceptable unacceptable 2,4-diamino-6- unacceptable unacceptable hydroxypyrimidine 3-sulfamoyl-L-alanine unacceptable unacceptable 1,2,3-triazole unacceptable unacceptable benzotriazole unacceptable unacceptable ammonium sulfamate acceptable acceptable ______________________________________
TABLE II ______________________________________ Tin Strip Copper Exo- NOx Example Formula Time Attack therm evolution ______________________________________ 1 28% nitric acid acceptable 8 micro no no 7% ferric inches nitrate per 20 g/L minute Sulfanilamide 2 28% nitric acid acceptable 10 no no 7% ferric micro nitrate inches 20 g/L 3-amino- per 5- minute methylisoxazole 3 28% nitric acid acceptable 9 micro no no 7% ferric inches nitrate per 20 g/L 4-amino- minute 1,2,4-triazole 4 28% nitric acid acceptable 9 micro no no 7% ferric inches nitrate per 20 g/L sulfamide minute 5 28% nitric acid acceptable 8 micro no no 7% ferric inches nitrate per 50 g/L ammonium minute sulfamate 6 28% nitric acid acceptable 8 micro yes no 7% ferric inches nitrate per 50 g/L sulfamic minute acid 7 28% nitric acid acceptable 150 no yes 7% ferric micro nitrate inches 20 g/L per benzotriazole minute ______________________________________
TABLE III ______________________________________ Ex- am- Tin Strip Copper Copper NOx ple Formula Time Attack Appearance evolution ______________________________________ 8a 28% nitric acceptable 8 semi- no acid micro bright 7% ferric inches pink nitrate per 20 g/L minute Sulfanilamide 8b 28% nitric acceptable 8 uniform, no acid micro reflective, 7% ferric inches bright nitrate per pink 20 g/L minute Sulfanilamide 0.2% hydrochloric acid 9a 28% nitric acceptable 10 semi- no acid micro bright 7% ferric inches pink nitrate per 20 g/L 3- minute amino-5- methylisoxazole 9b 28% nitric acceptable 10 uniform, no acid micro reflective, 7% ferric inches bright nitrate per pink 20 g/L 3- minute amino-5- methylisoxazole 0.2% hydrochloric acid 10a 28% nitric acceptable 9 semi- no acid micro bright 7% ferric inches pink nitrate per 20 g/L 4- minute amino-1,2,4- triazole 10b 28% nitric acceptable 9 uniform, no acid micro reflective, 7% ferric inches bright nitrate per pink 20 g/L 4- minute amino-1,2,4- triazole 0.2% hydrochloric acid 11a 28% nitric acceptable 9 semi- no acid micro bright 7% ferric inches pink nitrate per 20 g/L minute sulfamide 11b 28% nitric acceptable 9 uniform, no acid micro reflective, 7% ferric inches bright nitrate per pink 20 g/L minute sulfamide 0.2% hydrochloric acid 12a 28% nitric acceptable 8 semi- no acid micro bright 7% ferric inches pink nitrate per 50 g/L minute ammonium sulfamate 12b 28% nitric acceptable 8 uniform, no acid micro reflective, 7% ferric inches bright nitrate per pink 50 g/L minute ammonium sulfamate 0.2% hydrochloric acid 13a 28% nitric acceptable 8 non- no acid micro uniform, 7% ferric inches matte nitrate per pink 50 g/L minute sulfamic acid 13b 28% nitric acceptable 8 uniform, no acid micro reflective, 7% ferric inches- bright nitrate per pink 50 g/L minute sulfamic acid 0.2% hydrochloric acid 14a 28% nitric acceptable 150 semi- yes acid micro bright 7% ferric inches pink nitrate per 20 g/L minute benzotriazole 14b 28% nitric acceptable 150 uniform, yes acid micro reflective, 7% ferric inches bright nitrate per pink 20 g/L minute benzotriazole 0.2% hydrochloric acid ______________________________________
Claims (4)
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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US08/521,305 US5911907A (en) | 1995-08-30 | 1995-08-30 | Composition and method for stripping tin and tin-lead from copper surfaces |
US09/075,716 US5928529A (en) | 1995-08-30 | 1998-05-11 | Composition and method for stripping tin and tin-lead from copper surfaces |
US09/134,222 US5989449A (en) | 1995-08-30 | 1998-08-14 | Composition and method for stripping tin and tin-lead from copper surfaces |
Applications Claiming Priority (1)
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US08/521,305 US5911907A (en) | 1995-08-30 | 1995-08-30 | Composition and method for stripping tin and tin-lead from copper surfaces |
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US09/075,716 Continuation US5928529A (en) | 1995-08-30 | 1998-05-11 | Composition and method for stripping tin and tin-lead from copper surfaces |
US09/134,222 Continuation US5989449A (en) | 1995-08-30 | 1998-08-14 | Composition and method for stripping tin and tin-lead from copper surfaces |
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US09/075,716 Expired - Lifetime US5928529A (en) | 1995-08-30 | 1998-05-11 | Composition and method for stripping tin and tin-lead from copper surfaces |
US09/134,222 Expired - Lifetime US5989449A (en) | 1995-08-30 | 1998-08-14 | Composition and method for stripping tin and tin-lead from copper surfaces |
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US09/134,222 Expired - Lifetime US5989449A (en) | 1995-08-30 | 1998-08-14 | Composition and method for stripping tin and tin-lead from copper surfaces |
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Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6258294B1 (en) * | 1997-10-01 | 2001-07-10 | Morton International, Inc. | Composition for stripping solder and tin from printed circuit boards |
US20030132416A1 (en) * | 2001-10-11 | 2003-07-17 | Shipley Company, L.L.C. | Stripping solution |
US20070169330A1 (en) * | 2006-01-20 | 2007-07-26 | Hsieh Sen Wu | Method of recycling wasted printed-circuit-board |
CN107385443A (en) * | 2017-06-23 | 2017-11-24 | 中国船舶重工集团公司第七二五研究所 | A kind of corrosive agent and caustic solution for the detection of nickel-base alloy metallographic |
CN111748817A (en) * | 2020-07-10 | 2020-10-09 | 龙南鸿宇泰科技有限公司 | Tin stripping water additive |
CN112111741A (en) * | 2020-09-25 | 2020-12-22 | 深圳市祺鑫环保科技有限公司 | Tin stripping liquid copper protecting agent and tin stripping liquid |
US10955439B2 (en) * | 2019-03-12 | 2021-03-23 | International Business Machines Corporation | Electrochemical cleaning of test probes |
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ATE482303T1 (en) * | 2005-10-25 | 2010-10-15 | Atotech Deutschland Gmbh | COMPOSITION AND METHOD FOR IMPROVING ADHESION OF POLYMERIC MATERIALS ON COPPER OR COPPER ALLOY SURFACES |
JP5792284B2 (en) | 2010-04-15 | 2015-10-07 | アドバンスド テクノロジー マテリアルズ,インコーポレイテッド | How to recycle an aged printed circuit board |
AP2014007781A0 (en) | 2011-12-15 | 2014-07-31 | Advanced Tech Materials | Apparatus and method for stripping solder metals during the recycling of waste electrical and electronic equipment |
CN105714298B (en) * | 2016-03-23 | 2019-01-29 | 广东利尔化学有限公司 | It is a kind of based on sulfuric acid-molysite system etching agent and preparation method thereof |
RU2690871C1 (en) * | 2018-07-10 | 2019-06-06 | Алексей Игоревич Буянов | Selective etcher of multi-composite electrolytic coatings based on tin and lead |
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CN107385443A (en) * | 2017-06-23 | 2017-11-24 | 中国船舶重工集团公司第七二五研究所 | A kind of corrosive agent and caustic solution for the detection of nickel-base alloy metallographic |
US10955439B2 (en) * | 2019-03-12 | 2021-03-23 | International Business Machines Corporation | Electrochemical cleaning of test probes |
CN111748817A (en) * | 2020-07-10 | 2020-10-09 | 龙南鸿宇泰科技有限公司 | Tin stripping water additive |
CN112111741A (en) * | 2020-09-25 | 2020-12-22 | 深圳市祺鑫环保科技有限公司 | Tin stripping liquid copper protecting agent and tin stripping liquid |
Also Published As
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US5989449A (en) | 1999-11-23 |
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